Python is_valid = True/False Variables

Question

This is my first S.O. post!

I'm trying to learn Python with Murach's Python Programming- an excellent resource by the way...

Regarding the following code:

is_valid = True
customer_type = input('Enter customer type (r/w): ')
if customer_type == 'r' or customer_type == 'w':
    print(f'You entered: {customer_type}')
    # pass

else:
    print('Customer type must be "r" or "w".')
is_valid = False

I don't understand why the is valid True & False variables are required because the code appears to work fine when I comment them both out?

Thanks in advance!!

It seems like the variable does nothing in this code. Please upload the full code or the reason why you added them to the code. — Roy Avidan, Mar 25 '21 at 16:03
Agree, you dont need the `is_valid = ...` lines if that is all the code you have. — Selnay, Mar 25 '21 at 16:04
This is likely not the full code. `is_valid` isn't used in any of the processes that function here. Without seeing the full code, we can only speculate what `is_valid` does. However, I assume that it is to check if the input is valid or not. Maybe it's just setting it up for something that is later to come in the course? — gmdev, Mar 25 '21 at 16:04
It might make sense if `is_valid = False` is indented to be part of the `else` clause. — gofvonx, Mar 25 '21 at 16:05
Thanks for all the quick responses! That is the entire code from the example in my book. — Sam Tomanio, Mar 25 '21 at 16:08

score 0 · Answer 1 · answered Mar 25 '21 at 16:05

I think that the code should look like this:

is_valid = True
customer_type = input('Enter customer type (r/w): ')
if customer_type == 'r' or customer_type == 'w':
    print(f'You entered: {customer_type}')
    # pass

else:
    print('Customer type must be "r" or "w".')
    is_valid = False  # space here

Now is_valid value will show if you entered valid input or not. In this example it does not do anything. I think there may be other code related with this variable later in the book.

score 0 · Answer 2 · answered Mar 25 '21 at 16:26

This appears to be a code segment that determines whether the input is valid, prints an error message if it's not, and leaves that determination in is_valid for later code to use. A typical use is to repeat asking until the user makes a valid choice. In this case, you generally want the variable to be invalid, so that your loop condition "reads postivite":

invalid = True
while invalid:      # no extra operations in the condition
    # get input
    # validate input

Junaid · Answer 3 · 2021-03-25T16:15:04.837

-1

Yes, you are right this program will work completely fine without the is_valid variable. But to ensure that the user type either r or w we can use this is_valid variable using a while loop as follows

is_valid = True
while is_valid:
    customer_type = input('Enter customer type (r/w): ')
    if customer_type == 'r' or customer_type == 'w':
        print(f'You entered: {customer_type}')
    else:
        print('Customer type must be "r" or "w".')
        continue
    is_valid = False

edited Mar 25 '21 at 16:15

answered Mar 25 '21 at 16:08

Junaid

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1
15

You change `is_valid` after the loop. It is not going to finish – Yevhen Kuzmovych Mar 25 '21 at 16:12
sorry it was a typing error. I have adjusted it. Kindly take a look at it now – Junaid Mar 25 '21 at 16:15
Now it makes more sense. But not very intuitive as you are making `is_valid=False` when the input is actually correct. – Yevhen Kuzmovych Mar 25 '21 at 16:17
I guess in the question originally posted the is_valid variable does absolutely nothing. The only way it can be used in the code, if the input entered by the user is either r or w. Otherwise, it will ask for the user to enter a valid input and that actually serves the purpose. – Junaid Mar 25 '21 at 16:23
You can just initialize it to `False` and do a `while not is_valid`. And then make it `True` when the user's input **is valid**. – Yevhen Kuzmovych Mar 25 '21 at 16:32
Either way it is gonna ask the user for the correct input. The method you mentioned will return the same result as mine. I don't think there is any difference. – Junaid Mar 25 '21 at 16:41
I'm not saying there is a difference for the user. There is a difference for somebody who reads your code. – Yevhen Kuzmovych Mar 25 '21 at 16:57

Python is_valid = True/False Variables

3 Answers3